Signaling system



June 24, 1930. v J, c, SCHELLENG 1,768,269

S IGNALING SYSTEM Filed M y 1925 2 Sheets-Sheet 1 lh venl'or: John C. Sahel/erg.

June 24, 1930. .1. c. SCHELLENG 1,768,269

SIGNALING SYSTEM Filed May 15, 1925 2 Sheets-Shet 2 a Q 0 wail? F nu nu g 1' g In venfor: John CSche/leny.

Patented June 24, 1930 radiated.

UNITED STATES PATENT OFFICE JOHN G. SCHELLENG, OF MILLBURN, NEW JERSEY, ASSIGNOR, BY MESNE ASSIGN- MENTS, TO WESTERN ELECTRIC COMPANY, INCORPORATED, A CORPORATION OF NEW YORK SIGNALING SYSTEM Application filed May 13, 1925.. Serial m. 29,900.

This invention relates to signaling systems grid lead from the opposite end. The anode and more particularly to short wave translead is taken through the water jacket at mission apparatus. the center of the tube. As tubes operating In short wave transmitting apparatusfin push-pull relationship must have their particularly at high power, difficulty'is freanodes at different instantaneous potentials. quently experienced in maintaining the fre- 1t is necessary to connect the Water jaclzet frequencies employed. In apparatus of this 'sulating connections.

kind spurious oscillations of high frequency In order to avoid any spurious oscillations frequently occur due to' the inductance of that might otherwise occur with the tubes the leads and the capacity of the leads and operating in push-pull relationship, balother apparatus. ancing condensers are connected between the It is an object of this grid of each tube and the plate of the other vide a high power, short wave radio trans tube comprising a push-pull amplifier mitting apparatus capable of operating at whereby coupling due to the inherent casubstantially constant frequency. pacity of the tubes is minimized.

Another object of this invention is to pro- Vith the tubes connected in push-pull revide a system of the character described lation, spurious oscillations may be generadapted to operate relatively free from spuated, since the tubes so connected have a rious oscillations. parallel relationship as regards the genera- These objects and others To eliminate these uninvention to prothat a negligible impedance is presented to spurious oscillations in the grid-filament cirwhich is cuit and a high impedance is presented for ed in successive stages. and these oscillations in the plate-filament circuit. Either type of network will serve to prevent oscillations of undesired frequency as oscillations will not be produced pro transmission over long distances, it is advisvided a low impedance path is inserted beable to employ apparatus having leads as tween the gridand filament of the tube so short as possible and apparatus in which the that the po tent1al of the grids is prevented impulses of signal or control frequency to' produce a modulated high frequency current of com aratively low power then ampliii ent invention by employing a plurality of at that stages of amplification, each stage consisting anode and filament. r

of water-cooled space discharge tubes con- In order to simplify the mechanical connected in push-pull relationship. struction and the wiring of the above ap- In order to avoid coupling between the h lmprove the operating input and output circuits and between the ficharacterlstlcs, the

due to capacity current tical plane extending from the input end of flowing in the insulating portions of the the apparatus to the radiating system. Such tube at high frequencies, a special type of an arrangement prevents, to a large extent,

. tube is used in which the cathode leads are unbalanced electrical constants of the cirtaken from one end of the tube and the cuit. A push-pull arrangement is preferred will be pointed out with claims appended hereto,

for .the reason that a neutral lead is provided in which impedance or other changes may be made without aifecting .the operation -of the circuit as a push-pull repeater.

, invention,

undesired oscillations which occur denser 29 being at thesamepotentialas the formers 23 and 24 respectively.

Fig. 3 is an elevation, partly in section, of an amplifier unit used in the system shown in Fig. 2.

. Fig. 4 is a plan view of the amplifier unit shown in Fig. 3.

In Fig. 1 is shown a push-pull amplifier comprising space discharge tubes 25 having input and output circuits connected to trans- Reactance coil 28, connected across the grids of tubes 25, together: with condenser 29 and resistance 30, which-connects the center portlon of reactance 28 to ground, tend to suppress with the tubes operating in effective parallel relationship especially at high frequencies. Condenser 29 is of such value that the circuit, including the parallel opposing reactances halves of the c0il'28 which coto the grid filament circuit of the tubes, is tuned to the frequency at which the spurious or undesired oscillations occur. In a particular installation, this frequency was found to be of the order of 10,000 kilocycles.

Resistance 30 introduces a damping 1rnped' ance to these oscillations which tends to prevent their building up, or causes them to be dissipated as heat. The lead including concommon filament connection of the tubes for oscillations occurring with the tubes operatparallel,

ing in push-pull relationship, no current will tend to flow through this lead during normal operation. For oscillations which occur with the tubes operating, as generators 'in however, the path including the 30 will have the condenser 29 and resistance impressed entire grid filament potential across them and will act as a dissipating path as'above set forth.

with the tubes operating in push-pull relationship due to amplifier reacting upon the input circuit through coupling due to the herent capacthe output circuit of the and 43 which are designed ity of the tubes, is prevented by balancing condensers 26 connected between the grid of oscillations tend to occur in this circuit with the tubes operating in parallel relationship to a point below the frequency of the waves to be amplified and offers a high impedance to spurious oscillations.

In the system shown in Fig. 2, rectangle 1 is used to represent a source of modulated high frequency oscillations comprising either one or both modulated components with or without the unmodulated component which may be of the order of 2,000 to 6,000 kilocycles, Modulated high frequency current from this source is impressed upon amplifier 2 including tubes 25 constituting a stage of push-pull amplification through transformer 23. The secondary of transformer 23 is tuned by means of condensers 22 to the operating frequency. The high frequency path between pleted by the ground connection 21 at the midpoint of condensers 22. Grid polarizing potential is applied to tubes 25 from source 10 through potentiometers 11 and 12 by means of which the to the grids of the tubes may be independently adjusted. Filter 13 is designed to. suppress high frequency or other fluctuating the grid and filament is compotential applied or any high frequency currentswhich might be picked up by the leads from generator 10.

Choke coils 14 are used to prevent high frequency current from the. grid-filament circuit from being impressed upon source 1 Condensers 15 serve as' stopping condensers to enable the grids to be separately: adjusted. Coils 16 are tuned by condenser 17 to the frequency of any spurious oscillations which might tend to occur and which are conducted through condenser 17 and resistance 18 to ground, in a-manner similar-to that described in'connection with condenser 29 and resistance 30 in the. system shown in Fig. 1. Balancing condensers 19 are connected between the grids and anodes of tubes 25 in a manner similar to condensers 26 of Fig.1. t Filament heating current is supplied to the tubes from source 31 through transformers 32 and 33, respectively, Filters 34 and 35 are designed to prevent high frequency currents from being impressed upon the transformers and source 31Yfrom' the operat-' ing circuits. H Anode potential is supplied to tubes 25 from source 40 through antra and-coils 42 offer a high impedance to hi' h .frequeiiey currents.

direct current path for the anode current 0 high frequency i present in the anode leads from being apground. Choke plied to the secondaries of the transformers 32 and 33. The transformers are further protected by safety gaps and choke coils 46 which are includedin the connectionsbetween the secondaries of transformers 32 and 33 and ground. The safety gaps also prevent destructive arcs being formed should a break occur in the leads. Energy is transferred between amplifier 2 comprising tubes 25 and associated circuits and amplifier 3 which is similar in all respects to the above described stage of amplification by means of tuned coupling circuit 50 comprising transformers 51 and 52 and variable condenser 53 by means of which the secondary of transformers 51 and 52 are tuned to the desired operating frequency.

The primary windings of transformers 51 and 52 are connected to ground 55 to allow any charge that may accumulate upon the coils due to leakage of current from source 40 through condensers 56 to be conducted to coil 54 in the ground lead offers a high impedance path for spurious Anode potential is applied to 66 and 67 which are tuned by operative without this coil.

oscillations which would tend to occur were a low impedance path provided to ground. The use of the choke coil is necessitated by the ground connection. The secondary windings of transformers 51' and 52 are connected to ground 57 to provide a high frequency path between the grid and cathode of the tubes comprising amplifier 3. Blocking condensers 58 are used to permit the direct current potential of the grids to be separately adjusted. I

Amplifier 3 contains apparatus similar to that shown for amplifier 2 connected in a similar manner and is coupled to an antenna or radiating circuit 60 by means of trans,- formers 61 and 62 comprising, in connection with condenser 63, a tuned coupling circuit.

the space discharge devices of amplifier 3 from source 64 through filter 65 and variable inductances means of condenser 68 to the operating frequency. Ground lead 57 and choke coil 69 are for the same purpose in amplifier 3 as ground lead 55 and choke coil 54 in amplifier 2. Choke coil 59 in the lead to the space current source 64 is used to prevent a certain low frequency type of oscillation which was noted in a system The overhangmg turns of coils 66 and 67, that is, the turns not included in the cirpuit between the terminals of condenser 68, materially assist in preventing spurious high frequency oscillations and to stabilize the system although'no definite theory has been developed to explain these operations. 4 In the operation of this system, oscillations are prevented from occurring with the tubes operating in effective parallel relationship by means of coils 16 which are tuned by condenser 17 to be of low impedance to oscillations of this kind. This tends to prevent potential building up betweenthe grids and the filaments of the space discharge devices which will tend to force oscillations through the circuit. Certain oscillations hich do tend to occur, however, are suppr seed by various high impedance paths between the plates and filaments of the tubes such as that presented by coils 54, 42, 43, 69, 59 and the overhanging turns of coils 66 and 67. Spurious oscillationslof the push-pull type are prevented by balancing condensers 19, ex-- cept at very high frequencies where the inductive reactance of the loop circuit, comprising condensers 19, the internal capacities of tubes 25 and the leads, become large. Spurious oscillations of the order of 30,000 kilocycles .were noted under some circumstances and were eliminated by making the inductances of the loop negligible. .This was done by reducing the area of the loop, making the leads short and increasing the diameter of the leads.

Figs. 3 and 4 disclose the physical arrangement and construction of the elements of one of the amplifier units of Fig. 2. In Figs. 3 and 4 the space discharge tubes 25 have grid connections 71 extendin through the glass portions 72 at the top 0 the tubes and filament connections entering through glass portions 74 at the lower. end of the tubes. Circular anodes 75, including water jackets, provide supporting .means for the tubes. Cooling water is supplied to each tube through a rubber hose shown as coil 76 in the lower ortion ofthe container.

Each tube 25 is supported by means of insulators 77 the container 79 with conducting yoke 80 in which anode of the tube is clamped. Bal- 'ancing condensers 19 are supported from the anode connections of the tube by means of brackets 81. The anode connections of the tube are taken'by means of lead 82 from bracket through the side wall of the'container 79 from which it is separated by insuand 78 connecting the sides oflator 83. Coil 16,condensers 15 and 17, and

resistance 18 are supported at the top portion of the unit. Condensers 37 and 39 and inductances '38 comprise filters 34 and 35 of Fig. 2; A filament supply transformer 33 for each tube is placed below shield 70 which prevents currents being induced from the operating high transformer or have been found to 7 O In constructing the circuit as a whole, it is found advisable to arrange all the parts substantially symmetrically with respect to a vertical ,plane traversing the entire assembly in -orde"' th frequency apparatus into the" other apparatus below shield each amplifier stage and v 1 ing operations at 'from occurring. above described were employed to comductance of -20 Means tending to prevent the occurrence of each type of possible oscillation must be employed in such a manner as to not interfere with the prevention of oscillations of an other type. In the circuit herein described the theoretical'explanation of the operation of 'eachand every element can not be given. However, it appears that symmetry of design tends to prevent those oscillations 'which'm'ight result from an unbalanced cir- One. type of oscillation which occurs cuit. with the tubes operating in push-pull relationship is prevented by theuse of the condensers 19 and another type which occurs with the tubes operating in parallel relationship is prevented by the combined effects of condenser 17, resistance 18 and coils 16. The overhanging turns of coils (36 and 67 have an additional effect in preventing undesired oscillations. Coils 42 and 43 and coil 59 prevent oscillations of a frequency lower. than the operating frequency which tends to occur in the circuit and coils '54 and 69 prevent oscillations which would occur if a low impedance path to ground were provided.

This system was found'to be free from" spurious oscillations when the foregoing precautions were taken after a rigid test co1nprising applying full anode potential to the tubes and reducing the negative grid polarization to zero while no signals were impressed upon the'amplifiers from source 1. In this condition high plate currents flow in the circuit which would tend to produce spurious oscillations were they not prevented Before the various means pletely' prevent undesired oscillations durfull power, spurious oscillations occurred of sufficient power to melt the glass of the tubes and of the condensers by heating the leads.

In a particular instance, the. following values have been found desirable for certain elements. Coils 16 have a series aiding inmicrohenries as measure of'the tubes 25. Variable maximum capacity of 200 micromicrofarads. Resistance 18 is of the order of 200 ohms. Coils 54, 59 and 69 have an inductance of 100 microhenries. COils'66 and.67 have a total inductance of about 20 microhenries and one or two overhanging turns. Condenserv 68 has a maximum capacity of .150 micromiorofarads. The electrical constants of the other elementsmay be determined in accordance with known principles.

from grid to grid condenser 17 has a electrodes of the pair of the source of waves, path for, said. oscillations between the mid portion of said high impedance and the ground connections 'or grounded cathode eleranged Although this invention has been described as applied to a particular system it is not to be limited thereto but only in accordance with the scope of the invention as defined by the following claims.

What is claimed is: I

1. A high power transmission system including a source of high frequency waves and an amplifier therefor comprising a plurality of space discharge devices for use at such high frequency that parasitic oscillations tend to occur characterized in this, that the devices are connected in opposed relation with respect to the source of waves and that a dissipative path is provided for the parasitic oscillations whereby they are sub stantially suppressed. 2. A system in accordance with claim 1, characterized in this that the dissipative path consists of a big 1 impedance for parasitic oscillations connected between the grid devices arranged in opposed relation with respect to the source of waves and a low impedance path for said oscillations between the mid-portion of said higl'i impedance and the ground connections or. grounded cathode elements of said devices.

3. A high power transmission system including a, source of high frequency waves and an amplifier therefor comprising a plurality of space discharge devices for use at such high frequency that parasitic oscillations tend-to occur,- said devices being connected in opposed relation with respect to the source of waves, and a dissipative path for the parasitic oscillations. whereby they are substantially suppressed, said dissipative path consisting of a high impedance for-parasitic oscillations connected between 1 the grid electrodes of the pair of devices arranged in opposed relation with respect to mentsof said devices, said low impedance path comprising'a condenser and resistance 111 series. I

4. A system in accordance with claim 1 characterized 'in this, that the dissipative path consists of impedance elements so ar- 1 and adjusted that potentials of undesired or spurious character are prevented from building up, whereby oscillations due I to either the push-puli or parallel relation of the tubes are prevented. 1 5. A system in accordance with claim 1,

characterized in this, that the dissipative g path comprises a low impedance for parasitic oscillations in the input circuits of the devices whereby potentials are prevented .from building up and a high impedance for said oscillations in the output circuit of the and a low impedancev electrodes of the pair of devices arranged in opposed relation with respect to the source of waves, and a low impedance path for said oscillations between the mid portionof said high impedance and the ground connections or grounded cathode elements of said devices, and balancing condensers connected between the grid of each device and the anode of the other device comprising the push-pull amplifier, cooperatin dissipative path whereby coupling between the input and output circuits due to inherent capacity of the devices is avoided.

In a signaling system, a source of high frequency signal modulated waves, means for amplifying said waves comprising a plurality of space discharge devices arranged in push-pull relationship, and a low im edance path between the grid and thev cat ode of said devices for dissipating undesired oscillations.

S; In a signaling system, a source of high frequency signal modulated waves, means for amplifymg said waves comprising a plurality of water-cooled space discharge devices arranged in push-pull relationship, and means comprising electrostatic shields for preventing undesired oscillations in. said system.

9. In a signaling system, a source of high frequency signal modulated waves, means for amplifying said waves comprising a plurahtyofs ace dischargedevices arranged in push-p relationship and means comprising an electrostatic s 'eld surroundin said amplifier anda low' impedance path between the grid and the cat ode of'said tuligs Ifpr reventing undesired oscillations. nali system, a source of "fh f uenc signa modulated waves, me ii n s fo l amph fying said waves comprising a plurality of stages, each stage consisting 0 two s ace discharge tubes connected in ush-p relationship a cathode connection being at one end oi said tubes and a grid connection at the other end of said tubes, balancing condensers for preventingelectrostaticeoii- V pling between e input and output oircuihl of said tubes due to the internal capacity thereof, an electrostatic shield surrounding v with said pair of water cooled space a 'ghpower short wave radio sigeach of said stages of amplification, means for preventing spurious oscillations in said system for 'said' oscillations between the grid and filament. of said tubes and a high impedance path for said oscillations between the anode and filament of said tubes.

'" 11. In a high power short wave transmitting apparatus comprising a plurality of stages of amplification, each stage comprising a pair of space discharge tubes, means for preventing undesired oscillations in said system comprising a high impedance path for said oscillations between said tubes and a low impedance path for said oscillations between each of said tubes and ground.

12. In a high power short wave transmitting apparatus comprising a plurality of stages of amplification, each stage comprising a pair of space discharge tubes, -means for preventing undesired oscillations in said system comprising a high impedance for said oscillations connecting the grids of each pair of tubes, and a low impedance path comprising a condenser and resistance in series connecting the mid-point of said impedance and round.

13. Ina high power short wave radio transmitting system a plurality of stages of amplification, each stage comprising a dischar e tubes arranged in push-pull relationship said tubes having anodes, cathodes and control electrodes, cathode connections at one end of said tubes, control electrode connections at the other end of said tubes, a water jacket surrounding the anodes of said tubes, means for mounting said tubes comprising a yoke adapted to clamp said waterjacket, and supportin means for said yoke comprising a pair 0 insulating compression members ar- Y for said oscillations between a point of neutral potential for push-pull oscillations and ground.

15. In a push-pull amplifier comprisin a pair of three-electrode space discharge levices, means for preventm parasitic oscillations caused b said tu e's operating in parallel relations p comprising a high impedance path for oscillations occurring in aralleloperation and a low impedance path or oscillations occurring inpush-pull operation.

In witness whereof Ihereunto subscribe nzyname this 7 da of Ma A. D. 1925.

i JOfiN C. CHELLENG.

comprising a low impedance path' 

